The development in the field of wind energy installations is characterized by a size trend. This relates not only to the individual wind energy installation, but also to windparks, which are formed from ever greater numbers of wind energy installations that are becoming ever larger. The installed power, which is therefore rising to a major extent, is currently leading to difficulties in the on-shore area where most windparks, and in particular large windparks, are located, owing to the restricted capacity of the power transmission network. In order to allow an adequate supply quality to be maintained, windparks are subject to increasingly more stringent requirements for network compatibility.
One important criterion for safe operation on the network is voltage stability. This is even more important for high feed powers, that is to say in particular for windparks which are connected to high-voltage and extra-high-voltage networks. It is known that it is advantageous to feed a wattless component (in particular a capacitive wattless component) into the network, in order to support the voltage level. Further important criteria are the transmission capability of the networks, such as the current load capacity, connection criteria such as mains flicker, and other effects, such as network losses.
It is known for a measurement point for the volt-amperes to be provided at a point where the windpark is linked to the network, and for this to be compared with nominal presets for the power factor, by means of a windpark host computer (parkmaster) (EP-A-1 519 040, WO-A-01/73518). The parkmaster uses this to determine power factor or wattless-component nominal values for the individual wind energy installations. These implement the requirements by producing a greater or lesser wattless component. However, this results in a change in the voltages and currents on the lines and transformers in the windpark. A similar concept with distributed regulation has been proposed in EP-A-1 512 869. The known concepts have the disadvantage that, particularly in the case of wind energy installations which are located at the end of a long line in the windpark, undesirable voltage rises can occur, leading to instabilities. This can result in undesirable disconnection of individual wind energy installations, or even damage to converters.